The present invention relates to relatively sliding arrangements and more particularly, to such sliding arrangements for use in a sewing machine.
Generally, ceramic materials provide high hardness, low friction coefficients and low heat conductivity comparison with a metallic materials. In this regard, ceramic materials are available for relatively sliding component which are operated at low speed and low load, since significant temperature elevation does not occur at the friction or sliding portions or surfaces. However, if the sliding, or frictional, movement is performed at high speed and high load, temperature at the sliding portions, or friction zones, is elevated to have an abnormally high temperature, thus thermal seizure may occur at the friction, or sliding portions. Accordingly, if the friction or sliding portions are subject to high speed and high load, ceramic material is not an adequate surface due to its insufficient heat conductivity.
If the friction, or sliding, portion is one at which high speeds and high loads are common, in conventional devices, metallic sliding components are used with a great amount of lubrication oil being supplied to the frictional surfaces in order to prevent thermal seizure. However, another consideration must be made with respect to lubrication oil leakage due to the application of a large volume of lubrication oil. Particularly, in case of a sewing machine which deals with a cloth and, therefore, if the lubrication oil is scattered or splashed on the cloth, the resultant product would be rendered unsuitable for the market place.
To avoid this, various countermeasures are required causing an increase in production costs, such as precise control of the lubrication oil supply.